Reciprocating belt stratifier

ABSTRACT

Apparatus for the treatment of ores and other solid materials containing fractions of different density comprises a conveyor surface for conveying a suspension of the material upwardly against a downward flow of wash liquid, and shaking means for imparting a shaking motion to the surface to facilitate separation of the fractions contained in the material. In different embodiments, the apparatus comprises (a) washing means for supplying wash liquid to the surface in a dropwise fashion from above the surface at a series of positions spaced across the surface transversely to the direction in which the material is conveyed by the surface, (b) means for feeding the material on to the surface along each of those two sides thereof which are disposed in the general direction in which the material is conveyed by the surface (c) means for imparting a first orbital shaking motion to the surface to facilitate the initial separation of the fractions contained in the material and means for imparting a second orbital shaking motion to the surface of higher amplitude and/or lower frequency than the first to facilitate discharge of the lighter fractions from the surface.

United States Patent [1 1 Mozley RECIPROCATING BELT STRATIFIER [75] Inventor: Richard Henry Mozley, Walberton,

' near Arundel, England v .221 Filed: Be s, 1970 211 Appl. No.: 94,751

[30] Foreign Application Priority Data Dec. 5,1969 Great Britain 57,664/69 Mar. 11; 1970 Great Britain 11,692/70 Mar. 11, 1970 Great Britain 11,693/70 [52] US. Cl...;....' 209/433, 209/498, 209/500,

- r r r r 209/504 [51] Int. Cl B03b 3/00 [58] Field of Search; 209/433, 430, 470, 209/497, 498, 500, 504, 499

[56] 7 References Cited UNITED STATES PATENTS 884,636 4/1908 Buckingham 209/433 2,421,397 6/1947 Stewart 209/433 561,629 6/1896 7 Tulloch 209/433 885,692 4/1908 Evans et al. 209/432 2,966,262 12/1960 Hobart 209/157 X 1,740,504 1'2/1929 Gretencort.. 209/498 X 46,806 3/1865 Kustel 209/429 1,044,697 Senn 209/433 [451 July 10, 1973 1,934,812 11/1933 Mitchell ..209/429 Primary ExarriineF-Tirn R. Miles Assistant Examiner-Ralph J. Hill 7 Attornay-Cushman, Darby & Cushman ABSTRACT Apparatus for the treatment of ores and other solid materials containing fractions of different density comprises a conveyor surface for conveying a suspension of the material upwardly against a downward flow of wash liquid, and shaking means for imparting a shaking motion to the surface to facilitate separation of the fractions contained in the material. In different embodiments, the apparatus comprises (a) washing means for supplying wash liquid to the surface in adropwi'se fashion from above the surface at a series of positions spaced across the surface transversely to the direction in which the material is conveyed by the surface, (b) means for feeding the material on to the surface along each of those two sides thereof which are disposed in the general direction in which the material is conveyed by-the surface (c) means for imparting a first orbital shaking motion to the surface; to facilitate the initial separation of the fractions contained in the material lighter fractions from the surface. 1 r

31 Claims, 6 Drawing Figures l 3a If); (4

PAH-INTEL; JUL 1 0 ms sum 1 or 2 RECIPROCATING BELT STRATIFIER This invention relates to the treatment of ores and other solid materials, and more particularly to the separation of materials containing fractions distributed over a range of density.

The present invention is concerned especially with those types of separator, for example vanners, in which the heavier fractions in a suspension of material are washed free from the lighter fractions by means of a flow of washing liquid down an inclined, moving belt to the shaken surface of which the material is fed, the heavier fractions being retained on the belt and carried upwardly by it.

Whilst vanners have been used for many years in the treatment of suspensions, their efficiency does leave much to be desired. It has now been discovered that the grade and/or recovery achieved may be significantly bettered by improvements to the conventional form of vanner.

The efficiency of the conventionalvanner is limited by the necessity to balance the speed of the continuous belt with the amount of wash water used. Thus, for example, an increase in belt speed will lead to an imrpoved recovery of material, but unless the amount of wash water is also increased, the material recovered will be of a poor grade, and if the amount of wash water is in fact increased, this then leads to a poorer recovery. It has been found that it is possible substantially to overcome these difficulties and provide a vanner wherein the amount of wash water required at any given belt speed may be reduced as compared with the conventional vanner, thus giving rise to improvements in the grade and/or recovery which may be achieved.

According to the present invention apparatus for the treatment of ores and other solid materials containing fractions of different density comprises a conveyor surface for conveying a suspension of the material upwardly against a downward flow of wash liquid, shaking means for imparting a shaking motion to the surface to facilitate separation of the fractions contained in the material, and washing means for supplying wash liquid to the surface in a dropwise fashion from above the surface at a series of positions spaced across the surface transversely to the direction in which the material is conveyed by the surface.

causing the wash liquid to fall upon the conveyor sur-' face in a dropwise fashion it is possible to reduce fur? ther the quantity of wash liquid used by virtue of the greater separating effect produced by the increased momentum that is imparted to the liquid, thus leading to improved recoveries. It will be appreciated that in order to make the most effective use of the wash liquid the washing means will almost invariably be placed in a position, relative to that at which the material is fed to the surface, which is on that side towards which the material is carried by the motion of the conveyor.

Conveniently, the washing means is provided with a plurality of drop-forming devices which are preferably disposed in a linear fashion, most usually in a direction which is not only transverse but at right angles to the direction in which the material is carried by the motion of the conveyor. A higher quality of separation is generally achieved with the apparatus by the use of a plurality of washing means, for example two or three, spaced along the conveyor surface in the direction in which the material is conveyed by the surface. Best results are obtained by staggering the positions of the It will be appreciated that in addition to containing fractions of different density, the materials treated according to the present invention will usually contain particles of a range of sizes. Although apparatus according to this and other aspects of the invention might in rare instances be employed in the sizing of materials it is not primarily intended for this purpose and, indeed, it has been found, most particularly with apparatus according to the third aspect of the invention hereinafter described, that an advantage of the apparatus is its ability tof achieve a separation according to density even though a considerable range of sizes of particle is present in the material being separated.

It has been found that, contrary to general practice, separation of the fine gangue, only, should be attempted with the wash liquid, the shaking motion being relied upon to effect separation of the coarse gangue. This enables some reduction of the quantity of wash liquid used to be made but even so the amounts required when using a continuous stream of liquid usually still significantly reduce the recoveries obtained. By

drop-forming devices in any one series with respect to those of the adjacent washing means. Conveniently the spacing between adjacent drop-forming devices is uniform and preferably common to each of a plurality of washing means. A convenient spacing is from about 2 inches to about 6 inches, for example 4 inches, between adjacent drop-forming devices. When using a common spacing throughout a plurality of washing means, the staggering of drop-forming devices is optimal when each series is displaced along the washingmeans with respect to the adjacent series by one-half of the spacing between the drop-forming devices. Preferably the nature of the drop-fonning devices and their spacing, both along any washing means and between adjacent washing means, is such that the areas of turbulence produced by the drops of wash liquid on the conveyor surface are distinct. For example, the spacing between the dropping devices of a washing means may equal the spacing between adjacent washing; means and the dropping devices may be such as to produce a circular area of turbulence of diameter equal to one-half of this spacing. The height from which the wash liquid, which will almost invariably be water, is caused to fall upon the surface, depends on the nature of the suspension being treated and on the other variables in the operation of the apparatus. As a guide, however, a distance of fall for the drops of liquid on to the surface of from about 2" to about 6 inches, for example 4 inches, is usually satisfactory. Preferably the apparatus is provided with means for varying the height of the washing means above the surface.

The present invention includes a process for the treatment of ores and other solid materials containing fractions of different density which comprises feeding the material on to the surface of a conveyor which conveys a suspension of the material upwardly against a downward flow of wash liquid provided by washing means which supply wash liquidto the surface in a dropwise fashion from above the surface at a series of positions spaced across the surface transversely to the direction in which the suspension of material is con veyed by the surface, imparting a shaking motion to the surface to facilitate separation of the fractions contained in the material, and discharging the heavier fractions from the upper end of the surface and the lighter fractions from the lower end of the surface.

A variety of different means may be used for feeding the material on to the conveyor surface, but whichever method is used, the material is most usually in the form of a suspension before it is fed to the surface. The suspension is, however, preferably of high density and, in some instances, the material may even be fed to the surface in the dry state. It has been found that in general it is advantageous, particularly with the wider conveyors, to feed the material to surface in a diversified fashion rather than at one place only and, furthermore, to feed it directly on to the surface causing as little disturbance as possible.

One form of feeding which may be employed is endflow feeding, in which the material is fed to the surface along a line at right angles to the direction in which the material is conveyed by the surface. Conveniently, a plurality of feeding means may be employed, the positioning of individual means across the surface preferably being staggered in relation to the drop-forming devices of the washing means, or adjacent washing means where more than one is used. Conveniently, the spacing of the feeding means may be identical to that of the drop-forming devices of any washing means and the form of staggering may be that described as optimal between a plurality of washing means. As an alternative to the use of end-flow feeding, cross-flow feeding may be employed, in which the material is fed obliquely across the surface. It has been found, however, that another alternative method, double side-flow feeding, in which the material is fed along each of those two sides of the surface which are disposed in the general direction in which the material is conveyed by the surface, is usually to be preferred to either end-flow or crossflow feeding.

According, therefore, to a second aspect of the present invention apparatus for the treatment of ores and other solid materials containing fractions of different density comprises a conveyor surface for conveying a suspension of the material upwardly against a downward flow of wash liquid, shaking means for imparting a shaking motion to the surface to facilitate separation of the fractions contained in the material, and means for feeding the material on to the surface along each of those two sides thereof which are disposed in the general direction in which the material is conveyed by the surface.

The use of double side-flow feeding has the advantage that a substantial feed length may be achieved in a very convenient manner, so that for any given rate of flow of material on to the surface the velocity of the freshly added material over any banked or banking heavier fractions is minimised. It will be appreciated, for instance, that by feeding at each side along a length equal to the width of the conveyor the same rate of feed per minute can be achieved as when using cross-flow feeding across the width of the conveyor, but with only half the rate of feed per foot of length of the surface. Furthermore, whilst the construction and operation of conveyors of substantial width presents considerable problems, this is not true with those of substantial length.

The material is preferably fed over as great a length as conveniently possible, preferably along two straight lines, the lines most usually being of the same length and located opposite to each other. Almost invariably the sides of the conveyor are parallel and conveniently, the lines may be disposed parallel to the sides of the surface. The material may be fed on to the surface at two series of linearly spaced separate positions, or continuously along the straight lines. The former mode of feeding may be effected by the use of a tube with holes set along it at intervals whilst the latter mode may be effected by the use of a feed box of the type commonly used with slime tables. This type of box, incorporating a well into which a suspension of thematerial flows and from which it overflows into a series of channels which transfer it to the surface, provides a particularly convenient form of feeding means. It is important that the material is not given any appreciable component of motion towards the centre of the conveyor surface and the channels are thus conveniently set at a narrow angle, for example'from about 5 to about to the side of the conveyor and are directed towards the lower end of the conveyor.

it has been found that in apparatus according to the several aspects of this invention, it is advantageous to employ a conveyor surface which, in a direction transverse to that in which the material is conveyed by the surface, is lower at the centre than at the sides. Conveniently, however, the surface has this form only in the zone to which the material to be separated is fed, which may be referred to as the feed zone, and is substantially flat on either side of this zone. Although this requirement may be met by the use of a surface which in the feed zone has a slight downward curvature it is preferred, particularly with apparatus employing double side-flow feeding, rather to use a surface having a cross-section which is of a shallow V-shape. Conveniently the conveyor may be constructed from a material of a flexible nature and may be supported in the feed zone in a manner which provides the appropriate corss-sectional form for the surface. Although various support means may be employed a surface of V-shape cross-sectional form is provided conveniently by the use of pairs of rods pivoted centrally beneath the conveyor surface.

The use of a conveyor having a surface of V-shaped cross-section in the feed zone in combination with double side-flow feeding provides favourable conditions for obtaining a preliminary degree of separation as the material is fed on to the surface. Thus, the material to be separated flows from both sides of the conveyor slowly down the shallow incline towards the deeper fluid in the middle of the surface in the form of a thin film in which the conditions are such that a settling out of much of the finest of the heavier fractions occurs before the film mixes with the deeper fluid. It is found, in practice, that two such banks of settled heavier fractions are formed approximately one-third of the way in from each side of the conveyor to its centre. The de- 1 I gree of slope of each side of the conveyor surface down to its centre is preferably only slight, conveniently up to about 1, for example 1?, and it is convenient for the apparatus to be provided with means for altering the depth of the V-shaped channel in the surface.

The present invention also includes a process for the treatment of ores and other solid materials containing fractions of different density which comprises feeding the material on to the surface of a conveyor which conveys a suspension of the material upwardly against a downward flow of wash liquid, the material being fed on to the surface along each of those two sides thereof which are disposed in the general direction in which the material is conveyed by the surface, imparting a shaking motion to the surface to facilitate separation of the fractions contained in the material, and discharging the heavier fractions from the upper end of the surface and the lighter fractions from the lower end of the surface.

it will be appreciated that the use of double side-flow feeding is novel per se and that, although the method for the supply of wash liquid to the surface hereinbefore described is usually to be preferred, apparatus employing double side-flow feeding may, if desired, be used in connection with other methods for supplying wash liquid to the surface. Thus, for example, one alternative method involves the supply of wash liquid at positions spaced along a line substantially parallel to the direction in which the material is conveyed by the surface, and another particularly simple method which has been used with some advantage involves the supply of liquid in a controlled, but not dropwise, manner to the feed zone. Thus, a pair of passage means, for example,

two tubes, may conveniently supply a flow of wash liquid at either side of the surface. Such an arrangement has the advantage that it tends to crowd the settled heavier fractions towards the centre of the conveyor surface into a narrower and deeper band, this action having the desirable result of forcing any of the lighter fractions present to the upper surface of the band where they may be more readily washed back down the conveyor surface by the flow of wash water, thus producing a cleaner concentration of the heavier fractions.

The shaking motion imparted to the conveyor surface of apparatus having one or both of the features of dropwise supply of wash liquid or double sidefeed may take various forms, but whichever form is used the motion may conveniently be substantially in the plane of the surface. In general, however, the motion is preferably of an orbital nature. Furthermore, it has been found that it is preferable for an orbital motion to be experienced over the whole surface. A particularly convenient way of imparting an orbital shaking motion to the conveyor surface is for the conveyor to be mounted in a freely suspended framework and for an out-ofbalance shaft to be mounted on the framework. It will be appreciated, however, that if the shaft is mounted near one end of the conveyor the motion experienced at the far end thereof is essentially linear in nature and it is therefore preferred that the shaft is mounted on the framework in the region of the centre of the conveyor. It has been found, however, that by imparting not one but two orbital shaking motions to the surface particularly satisfactory results are obtained, a significantly im roved efficiency of discharge of coarse gangue from the iower end of the conveyor surface being achieved.

According, therefore, to a third aspect of the present invention apparatus for the treatment of ores and other solid materials containing fractions of different density comprises a conveyor surface for conveying a suspension of the material upwardly against a downward flow of wash liquid, means for imparting a first orbital shaking motion to the surface to facilitate the initial separation of the fractions contained in the material and means for imparting a second orbital shaking motion to the surface of higher amplitude and/or lower frequency than the first to facilitate discharge of the lighter fractions from the surface.

By the amplitude of the first or second orbital motion, the maximum amplitude of the individual motion him] motion is imparted to the surface at one particular position other-than centrally the amplitude of the, motion experienced at any point on the surface duetothat orbital motion will vary. The frequency of the first or second orbital motion similarly applies to that of the individual motion.

The application of two separate shaking motions to the conveyor surface has the advantage that it enables different motions to be imparted to the surface appropriate to the different types of separation taking place thereon. Thus the first orbital shaking motion, which is preferably of both relatively lower amplitude and higher frequency, is suitable at the upper end of the surface where deposition of the bulk of the heavier fractions occurs and where removal of the lighter fractions from these heavier fractions takes place in the washing zone, whilst the second orbital motion, which is preferably of both relatively higher amplitude and lower frequency, is suitable at the lower end of the surface in order to achieve efficient discharge of the coarser of the lighter fractions from the surface without preventing or significantly retarding the deposition on the surface of the finer of the heavier fractions still remaining in suspension.

Whilst the shaking motions may be applied at the same point of the conveyor surface, for example, centrally so that an orbital motion is experienced over the whole surface, it is preferred that the shaking motions are applied at positions spaced apart in the direction of that end for which the type of motion imparted is appropriate. Thus, the apparatus may be provided with means for imparting a first orbital shaking motion between the centre of ;the surface and that end of the surface towards which the material is. conveyed or, preferably, at the centre of the surface itself, and with means for imparting a second orbital shaking motion at that end of the surface away from which the material is conveyed by the surface or between that end and the centre of the surface.

The ratio of the two amplitudes (i.e. of the maximum amplitudes) may be from about 1:8 to about 5:8, conveniently from about 1:4 to about 1:2, for example 3:8, and the ratio of the two frequencies may be from about 4:1 t about 4:3, conveniently from about 3:1 to about 3:2, or example 2:]. The optimum values for the amplitudes and frequencies will depend on the particular use being made of the apparatus but, as a guide, a first orbital motion with an amplitude (i.e. maximum amplitude) of up to about three-fourths inch, preferably from about one-eighth inch to about five-eighth inch, and a frequency of from about 200 to about 400 r.p.m., preferably from about 250 to about 350 r.p.m., in combination with a second orbital motion with an amplitude of from about three-fourth inch to about 3 inches, preferably from about 1 inch to about 2 inches, and a frequency of from about 50 to 250 r.p.m., preferably from about to 200 rpm, is suitable for many forms of separation.

In common with other forms of shaking motion, it has been found that for the most effective separation of material on the surface at least one of the orbital shaking motions and preferably both of them are substantially in the plane of the surface. Furthermore, although one or both of the shaking motions may be asymmetric, it is preferred that they are both symmetric about the central axis of the conveyor surface running in the direction in which material is conveyed by the surface. The orbital shaking motions may be provided in various ways, for example by the use of cranked shaking shafts. A particularly convenient method of providing the shaking motions, however, is for the conveyor to be mounted in a freely suspended framework and for the shaking motions to be provided by out-of-balance shafts mounted on the framework, for example, either in a concentric fashion or separately along said central axis of the conveyor surface. The shaft providing the second orbital motion may, if desired, be'mounted outside the framework beyond the end away from which the material is conveyed by the conveyor surface. It will be appreciated that since a motion applied by a shaft mounted on a framwork occurs in a plane at right anglesto the suspension system of the framework, the motion will be actually in the plane of the conveyor sur face when the surface is horizontal, but with inclinations of the magnitude of those used with the apparatus, the motion will always be substantially in the plane of the surface.

For greater versatility the apparatus may be provided with means for varying the amplitude and/or frequency of one, and conveniently both, of the orbital shaking motions imparted to the surface of the conveyor.

It will be appreciated that the use of a first and second orbital motion of the type described is novel per se and that, although the methods for the supply of the wash liquid and the material to the surface that are usually preferred are those described as the first and second aspects of this invention, apparatus employing shaking means of this type may, if desired, be used in connections with other methods for the supply of wash liquid and material.

The present invention also comprises a process for the treatment of ores and other solid marials containing fractions of different density which comprises feeding the material to the surface of a conveyor which conveys a suspension of the material upwardly against a downward flow of wash liquid, imparting to the surface a first orbital shaking motion to facilitate the initial separation of the fractions contained in the material and a second orbital motion of higher amplitude and/or lower frequency that the first to facilitate discharge of the lighter fractions from the surface, and discharging the heavier fractions from the upper end of the surface and the lighter fractions from the lower end of the surface.

The conveyor section of the apparatus may assume conventional form being a continuous belt which is driven by a driving roller preferably at a variable speed. Conveniently, the driving roller may extend for the width of the conveyor and the conveyor may be-provided with a similar idler roller at its lower end. Although various conveyor speeds may be used, a speed of from about inches to about 50 inches per minute, often in the lower part of this range, is found to be suitable for many applications in combination, particularly when 'using a single washing means of the type describedin the first aspect of the invention, with a flow of wash liquid of from about 150 to about 350, for example 250, ml/minute/foot of width of the conveyor. The speed of the conveyor is, however, matched not only to the flow of wash liquid used but also to the frequency of the shaking motion imparted to the surface,

lower speeds usually being combined with lower frequencies.

Most conveniently, the apparatus is provided with means for varying the inclination of the surface of the conveyor to the horizontal, thus making possible selection of the optimum inclination appropriate to any particular use to which the apparatus is applied. Inclinations of from about one-half to 1 are found to be most useful although, particularly with coarse materials, greater inclinations, for example of up to about 5, may be used. The variation of the inclination of the surface to the horizontal may be carried out very readily when the conveyor is mounted in a framework suspended on wires, the inclination then being easily adjustable by alteration of the lengths of the wire or wires of one'end of the framework. Although a conveyor may be used which in use has a continuously inclined surface, it has been found that an improved separation is achieved by the use of a conveyor surface which in use is inclined at a relatively larger inclination to the horizontal above the feed zone than in the feed zone itself and below it. Thus the surface may be inclined, in use, at an angle of up to about 2, for example from about one-half to about 1, from the lower edge of the conveyor to the top of the feed zone and may be inclined at an angle of from about 2 to about 5 times as much, within the range from about 2 to about 5, from the top of the feed zone to the upper edge of the conveyor. Occasionally the lower part of the surface may be inclined at an even greater angle, for example of up to about 5, and the inclination of the upper part of the surface is then increased proportionately although usually by a ratio which is closer to 1:2 than 1:5. When using a surface of V-shaped cross-section as hereinbefore described it is preferred that the level of the centre of the V in the feed zone may conveniently be maintained on the same line of inclination as the substantially flat area below the feed zone. The increased inclination above the feed zone may readily be achieved by using a conveyor system in which it is the bottom roller that is driven so that the upper surface of the conveyor is under only very slight tension, and by providing support for the surface only up to the end of the feed zone and positioning the upper roller appropriately to cause an increased inclination of the surface above the feed zone. Conveniently both the overall inclination of the conveyor surface and the increased inclination of its upperportion are adjustable. The use of a relatively steep inclination up to the upper roller does mean, however, that the amount of liquid coming off the top of the conveyor surface is reduced and efficient means are therefore required for removing the heavier fractions from the surface, for example a scraper and/or water jets, the latter being of more value with the larger forms of the apparatus.

The processes of the present invention may be used for the treatment of a wide variety of mixtures of materials. They are, however, of particular value for the recovery of particles of a size below about 25 microns, which are difficult to handle by conventional methods, for example using slime tables. One field of application of this type is the treatment of slimes from tin mines, particularly those from which the tin present as larger particles has been extracted but which still contain valuable tin in the form of smaller particles.

The processes may be operated continuously, the

lighter fractions being continuously discharged from the lower edge of conveyor surface whilst the heavier fractions are continuously discharged from its upper edge. Under the correct conditions of shake and addition of wash liquid the lighter fractions are carried off the surface by the flow of liquid and may be collected by suitably situated collecting means.

The invention is illustrated by the accompanying drawings which are diagrammatic in nature and not to scale, of which:

FIG. 1 is a plan view of the apparatus (FIG. 1a showing a detailed view of a feed box of the apparatus);

FIG. 2 is a sectional view of the apparatus on the line II II of FIG. 1 (FIGS. 2a and 2b showing details of this view); and

FIG. 3 is a side view of the apparatus.

The apparatus shown in the Figures comrpises a continuous conveyor belt I of reinforced plastics material which passes over an upper idler-roller 2 and a lower driving-roller 3 mounted at opposite ends of a subframe 4. The roller 2 is adjustably mounted in slots 5 formed vertically in the sides of the sub-frame 4 so that its position in the sub-frame 4 may be varied. The di rection of movement of the belt 1 is in a clockwise direction as viewed in FIG. 2.

The belt 1 during its upward movement below the feed zone rests upon and is supported to provide a substantially flat surface by transverse metal rods 6 adjustably attached through bolts 7 and washers 8 to the sub frame 4. In the feed zone itself, the belt 1 rests upon and is supported to provide a surface 9 having a shallow V cross-section by pairs of transverse metal rods 10 pivoted near one end at 11 about the central longitudinal axis of the belt 1 and adjustably attached through bolts 12 and washers 13 to the subframe 4. The number of washers 8 beneath the rods 7 is generally adjusted so that the level relative to the sub-frame of the tops of the rods 7 is equal to that of the tops of the rods 10 at their pivot point 11. The roller 2, however, is generally positioned at a higher level than this and, since the upper surface of the belt 1 is not tensioned to a significant extent, the belt therefore inclines upwards from the end of the feeding zone to the upper roller 2.

Mounted transversely on the sub-frame 4 are two collecting troughs 14 and 15 positioned beneath each of the rollers 2 and 3 for collecting the heavier fractions and higher fractions respectively. The lower surface 16 of the belt '1 contacts a scraper 17 mounted transversely on the sub-frame 4 above the trough 14.

The sub-frame 4 is suspended from a fixed frame 18 (part of which only is shown in the Figures) by means of two pairs of suspension wires 19 and 20 attached to the upper and lower ends respectively of the sub-frame 4. The length of the wires 20 may be varied through adjustments of the screws 21 thus altering the inclination of the surface 9 to the horizontal.

Attached to. the sub-frame 4, beneath the belt 1, is a variable speed electric motor 22 which drives two sets of pulley wheels 23 and 24. The lower-set of pulley wheels 24 drives a shaft 25, mounted on the sub-frame 4, through a belt 26 connecting with a set of pulley wheels 27 mounted on the lower end of the shaft 25. The upper end of the shaft carries a pulley wheel 28 which drives a considerably larger pulley wheel 29 through a belt 30, the wheel 29 in turn driving the lower roller 3 through a gear box 31. The upper set of pulley wheels 23 drives two shafts 32 and 33, mounted beneath the belt 1 centrally and near the lower end of the sub-frame 4 respectively, through belts 34 and 35 which connect with pulley wheels 36 and 37 of equal size mounted on the lower ends of the shafts 32'and 33 respectively. The shaft 32 is driven from a larger pulley wheel 23 than the shaft 33 and thus rotates faster. The shafts 32 and 33 are provided with shake arms 38 and 39 on which are adjustably mounted shakeweights 40 and 41, respectively, the mass of the weight 40 being half that of the weight 41.

Mounted opposite each other on the fixed frame 18 are two feed boxes 42 for feeding the material to be spearated on to the surface 9 of the belt 1. The feed boxes 42 comprise a container portion 43 into which a suspension of the material is fed through tubing 44 at a rate controlled by the valve 45, and four channel portion 46 into which the suspension overflows from the container portion 43 and down which it flows on to the belt. The channel portions 46 are arranged at a narrow angle 10) to the longitudinal axis of the belt 1. The length of the feed zone is equal to the width of the belt whilst the ratio of the distances upper roller 2 to the top end of feed zone feed zone lower end of feed zone to lower roller 3 is 2 4 z 3. Suspended from a bridge 47 which is mounted on the fixed frame 18, are two tubes 48 and 49 to which wash water is supplied through the flexible tubes 50 and 51 at a constant rate determined by adjustment of the valve 52. Each of the tubes 48 and 49 is suspended from the bridge 47 by a pair of screw-threaded rods 53, the two tubes 48 and 49 being placed at the same distance perpendicularly above the surface of the belt 1. The rods 53 fit into holes 54 in the bridge 47 and are held in place by nuts 55 bearing on the bridge 47. By loosening the nuts 55 and moving the rods 53 into or out of the holes 54 the height of the tubes 48 and 49 can be varied. Formed in the top of the tubes 48 and 49 area series of holes 56 evenly spaced apart by the same distance that separates the tubes 48 and 49. In order to provide a clean separation of drops of wash water from the holes 56, wire drip points 57 (not shown for reasons. of simplicity in FIG. 2a) are positioned on the tubes 48 and 49 at each of the holes 56.

In operation, the length of the wires 20 is adjusted through the screws 21 and the vertical position of the roller 2 in the slots 5 is also adjusted to providesuitable upward inclinations of the conveyor belt 1 both up to the end of the feed zone and above it. The tubes 48 and 49 are adjusted to the required height above the surface of the belt 1 and the positions of the shake weights 40 and 41, on the shake arms 38 and 39 are then ad justed to provide orbital shaking motions of the required amplitude. The belt 26 is positioned between the set of pulley sheels 24 and the set 27 to give an appropriate speed of rotation, as compared with the speed of the motor 22, to the pulley wheel 28, and thus to the pulley wheel 29 and the lower roller 3. The motor 22 is switched on and adjusted to an appropriate speed so that theshake weights 40 and 41 and the lower roller 3 are rotating at the required frequency. The supply of water to the tubes 48 and 49 is then turned on and the rate of flow of water from the tubes 48 and 49 on to the conveyor belt 1 is adjusted through the valve 52 (if desired the belt 1 may first be treated with a wetting agent). Finally the feeding of the aqueous suspension of material to be separated on to the surface 9 of the belt 1 from the feed boxes 42 is started, the rate of feed being adjusted through the valve 45.

It will be appreciated that it will not always be possible to initially adjust all of the various variable parame ters to give the optimum conditions for a separation. More usually, those variables for which the adjustment required is accurately known beforehand will be adjusted to the values required and the rest will initially be set at an approximate value and adjusted further as the separation proceeds.

When the machine has reached a steady state a continuous separation is achieved, the lighter fractions being carried in suspension down the belt 1 by the wash water and collected in the trough 15 whilst the heavier fractions, which are usually those which are wanted, accumulate on the belt 1 and are discharged from its lower surface 16 into the trough 14 by the action of the scraper 17.

I claim:

1. A process for the treatment of ores and other solid materials containing fractions of different density which comprises feeding said material to the surface of a conveyor which conveys a suspension of the material upwardly against a downward flow of wash liquid, im-

parting to the surface a first orbital shaking motion to facilitate an initial separation of the fractions contained in the material and a second orbital motion of lower frequency and optionally higher amplitude than the first to facilitate discharge of the lighter fractions from the surface, and discharging the heavier fractions from the upper end of the surface and the lighter fractions from the lowerend of thesurface.

2. Process according to claim 1 wherein the second orbital shaking motion is of both lower frequency and higher amplitude than the first.

3. Process according to claim 2 wherein the ratio of the frequencies is in the range from 4:1 to 4:3 and the ratio of the amplitudes is in the range from 1:8 to 5:8.

4. Process according to claim 1 wherein the ratio of the frequencies is in the range from 4:1 to 4:3.

5. Process according to claim 1 wherein the ratio of the amplitudes is in the range from 1:8 to 5:8.

6. Process according to claim 1 wherein the wash liquid is supplied to the surface in a dropwise fashion from above the surface at .a series of positions spaced across the surface transversely to the direction in which the material is conveyed by the surface.

7. Process according to claim 6 wherein the wash liquid is supplied at a plurality of series of positions, said series being spaced along the surface in the direction in which the material is conveyed by the surface and the positions of each series being staggered in a direction transverse to that in which the material is conveyed by the surface with respect to the positions of immediately adjacent series.

8. Process according to claim 1 wherein the material is fed to the surface as a liquid suspension.

9. Process according to claim 8 wherein the material comprising a movable frame, a conveyor carried by said frame and providing a surface for conveying a suspension of said material upwardly against a downward flow of wash liquid, means for imparting a first orbital shaking motion to the frame to facilitate an initial separation on said surface of the fractions contained in the material and means for imparting a second orbital shaking motion to the frame of lower frequency than the first to facilitate discharge from the surface of the lighter fractions.

13. Apparatus according to claim 12 wherein the ratio of the frequencies is in the range from 4:1 to 4:3.

14. Apparatus according to claim 12 wherein the second orbital shaking motion is of higher amplitude than the first.

15. Apparatus according to claim 14 wherein the ratio of the amplitudes is from l:8 to 5:8.

16. Apparatus according to claim 14 comprising means for varying the amplitude of the shaking motion or motions.

17. Apparatus according to claim 15 wherein the ratio of the frequencies is from 3:1 to 3:2 and the ratio of the amplitudes is from 1:4 to 1:2.

18. Apparatus according to claim 12 comprising means for varying the frequency of the shaking motion or motions.

19. Apparatus according to claim 12 wherein the orbital shaking motions are imparted to the frame at positions spaced apart in the direction in which the material is conveyed by the conveyor surface, the first orbital motion being imparted at a position intermediate to the ends of the conveyor and between that end of the conveyor towards which the material is-conveyed by the surface and the position at which the second orbital motion is imparted.

20. Apparatus according to claim 19 wherein the first I orbital motion is imparted at the center of the surface,

is fed on the surface along each of those two sides with respect to the direction in which material is conveyed by the surface, while the second orbital motion is imparted at that end of the conveyor away from which the material is conveyed by the surface.

21. Apparatus according to claim 19 wherein the first orbital motion is imparted between the center of the surface, with respect to the direction in which the material is conveyed by the surface, while the second orbital motion is imparted at that end of the conveyor between the conveyor end and the center of the surface.

22. Apparatus according to claim 12 wherein the shaking motions are substantially in the planevof the surface.

23. Apparatus according to claim 22 wherein the frame is freely suspended and said shaking means comprise out-of-balance shafts located on said frame centrally to the conveyor surface with respect to a direction transverse that in which material is conveyed by the surface.

24. Apparatus according to claim 12 having means for varying the inclination of the conveyor surface to the horizontal.

25. Apparatus according to claim 12 comprising washing means for supplying wash liquid to the surface in a dropwise fashion from above the surface at a series of positions spaced across the surface transversely to the direction in whichthe material is conveyed by the surface.

26. Apparatus according to claim 25 having washing means for supplying wash liquid at a plurality of series of positions, said series being spaced along the surface in the direction in which the material is conveyed by the surface and the positions of each series being staggered in a direction transverse to that in which the material is conveyed by the surface with respect to the positions of immediately adjacent series.

27. Apparatus according to claim 26 wherein the washing means comprise a plurality of series of linearly disposed drop-forming devices disposed at right angles to the direction in which the material is conveyed by the surface.

28. Apparatus according to claim 12 comprising means for feeding the material on to the conveyor surface along each of those two sides thereof which are disposed in the general direction in which the material is conveyed by the surface.

29. Apparatus according to claim 28 wherein th feeding means is adapted for feeding of a liquid suspension of the material to the surface in a direction which is substantially opposite to that in which the material is conveyed by the surface.

30. Apparatus for the treatment of ores and other solid materials containing fractions of different density comprising, t

a movable frame,

a conveyor carried by said frame and providing asur face for conveying a suspension of said material upwardly against a downward flow of washliquid,

means fur supplying wash liquid to the surface in a dropwise fashion from above the surface at a plurality of series of positions, the series being spaced along the surface in the direction in which material is conveyed by the surface, and,the positions of each series being spaced acrossthe surface transversely to the direction in which material is conveyed by the surface and being staggered in said transverse direction with respect to the positions of immediately adjacent series,

means for imparting a first orbital shaking motion to the frame to facilitate an initial separation on the surface of the fractions contained in the material,

and means for imparting a second orbital shaking 

1. A process for the treatment of ores and other solid materials containing fractions of different density which comprises feeding said material to the surface of a conveyor which conveys a suspension of the material upwardly against a downward flow of wash liquid, imparting to the surface a first orbital shaking motion to facilitate an initial separation of the fractions contained in the material and a second orbital motion of lower frequency and optionally higher amplitude than the first to facilitate discharge of the lighter fractions from the surface, and discharging the heavier fractions from the upper end of the surface and the lighter fractions from the lower end of the surface.
 2. Process according to claim 1 wherein the second orbital shaking motion is of both lower frequency and higher amplitude than the first.
 3. Process according to claim 2 wherein the ratio of the frequencies is in the range from 4:1 to 4:3 and the ratio of the amplitudes is in the range from 1:8 to 5:8.
 4. Process according to claim 1 wherein the ratio of the frequencies is in the range from 4:1 to 4:3.
 5. Process according to claim 1 wherein the ratio of the amplitudes is in the range from 1:8 to 5:8.
 6. Process according to claim 1 wherein the wash liquid is supplied to the surface in a dropwise fashion from above the surface at a series of positions spaced across the surface transversely to the direction in which the material is conveyed by the surface.
 7. Process according to claim 6 wherein the wash liquid is supplied at a plurality of seRies of positions, said series being spaced along the surface in the direction in which the material is conveyed by the surface and the positions of each series being staggered in a direction transverse to that in which the material is conveyed by the surface with respect to the positions of immediately adjacent series.
 8. Process according to claim 1 wherein the material is fed to the surface as a liquid suspension.
 9. Process according to claim 8 wherein the material is fed on the surface along each of those two sides thereof which are disposed in the general direction in which the suspension of material is conveyed by the surface.
 10. Process according to claim 1 wherein the material is a mineral pulp or slime.
 11. Process according to claim 10 wherein the pulp or slime contains a tin ore, the heavier fractions thereof being of higher tin content.
 12. Apparatus for the treatment of ores and other solid materials containing fractions of different density comprising a movable frame, a conveyor carried by said frame and providing a surface for conveying a suspension of said material upwardly against a downward flow of wash liquid, means for imparting a first orbital shaking motion to the frame to facilitate an initial separation on said surface of the fractions contained in the material and means for imparting a second orbital shaking motion to the frame of lower frequency than the first to facilitate discharge from the surface of the lighter fractions.
 13. Apparatus according to claim 12 wherein the ratio of the frequencies is in the range from 4:1 to 4:3.
 14. Apparatus according to claim 12 wherein the second orbital shaking motion is of higher amplitude than the first.
 15. Apparatus according to claim 14 wherein the ratio of the amplitudes is from 1:8 to 5:8.
 16. Apparatus according to claim 14 comprising means for varying the amplitude of the shaking motion or motions.
 17. Apparatus according to claim 15 wherein the ratio of the frequencies is from 3:1 to 3:2 and the ratio of the amplitudes is from 1:4 to 1:2.
 18. Apparatus according to claim 12 comprising means for varying the frequency of the shaking motion or motions.
 19. Apparatus according to claim 12 wherein the orbital shaking motions are imparted to the frame at positions spaced apart in the direction in which the material is conveyed by the conveyor surface, the first orbital motion being imparted at a position intermediate to the ends of the conveyor and between that end of the conveyor towards which the material is conveyed by the surface and the position at which the second orbital motion is imparted.
 20. Apparatus according to claim 19 wherein the first orbital motion is imparted at the center of the surface, with respect to the direction in which material is conveyed by the surface, while the second orbital motion is imparted at that end of the conveyor away from which the material is conveyed by the surface.
 21. Apparatus according to claim 19 wherein the first orbital motion is imparted between the center of the surface, with respect to the direction in which the material is conveyed by the surface, and that end of the conveyor towards which material is conveyed while the second orbital motion is imparted between that end of the conveyor away from which the materials is conveyed by the surface and said center of the surface.
 22. Apparatus according to claim 12 wherein the shaking motions are substantially in the plane of the surface.
 23. Apparatus according to claim 22 wherein the frame is freely suspended and said shaking means comprise out-of-balance shafts located on said frame centrally to the conveyor surface with respect to a direction transverse that in which material is conveyed by the surface.
 24. Apparatus according to claim 12 having means for varying the inclination of the conveyor surface to the horizontal.
 25. Apparatus according to claim 12 comprising washing means for supplying wash liquid to the sUrface in a dropwise fashion from above the surface at a series of positions spaced across the surface transversely to the direction in which the material is conveyed by the surface.
 26. Apparatus according to claim 25 having washing means for supplying wash liquid at a plurality of series of positions, said series being spaced along the surface in the direction in which the material is conveyed by the surface and the positions of each series being staggered in a direction transverse to that in which the material is conveyed by the surface with respect to the positions of immediately adjacent series.
 27. Apparatus according to claim 26 wherein the washing means comprise a plurality of series of linearly disposed drop-forming devices disposed at right angles to the direction in which the material is conveyed by the surface.
 28. Apparatus according to claim 12 comprising means for feeding the material on to the conveyor surface along each of those two sides thereof which are disposed in the general direction in which the material is conveyed by the surface.
 29. Apparatus according to claim 28 wherein the feeding means is adapted for feeding of a liquid suspension of the material to the surface in a direction which is substantially opposite to that in which the material is conveyed by the surface.
 30. Apparatus for the treatment of ores and other solid materials containing fractions of different density comprising, a movable frame, a conveyor carried by said frame and providing a surface for conveying a suspension of said material upwardly against a downward flow of wash liquid, means fur supplying wash liquid to the surface in a dropwise fashion from above the surface at a plurality of series of positions, the series being spaced along the surface in the direction in which material is conveyed by the surface, and the positions of each series being spaced across the surface transversely to the direction in which material is conveyed by the surface and being staggered in said transverse direction with respect to the positions of immediately adjacent series, means for imparting a first orbital shaking motion to the frame to facilitate an initial separation on the surface of the fractions contained in the material, and means for imparting a second orbital shaking motion to the frame of lower frequency and optionally higher amplitude than the first to facilitate discharge from the surface of the lighter fractions.
 31. Apparatus according to claim 30 comprising means for feeding the material on to the conveyor surface along each of those two sides thereof which are disposed in the general direction in which the material is conveyed by the surface. 